In recent years, many advances in the area of electroplating of copper deposits have produced increasingly superior properties in ductility, leveling and other properties of copper deposits produced from high metal low acid electroplating baths. Primarily, these advances have been in the use of various additions to such copper electroplating baths. Most notably, the additions of divalent sulfur compounds and alkylation derivatives of polyethylene imines have resulted in improved leveling in decorative copper plating. Examples of these types of additions are shown in U.S. Pat. No. 4,336,114 to Mayer et al.; U.S. Pat. No. 3,267,010 to Creutz et al.; U.S. Pat. No. 3,328,273to Creutz; U.S. Pat. No. 3,770,598 to Creutz et al.; and U.S. Pat. No. 4,109,176 to Creutz et al. While these additions have found commercial acceptance in plating of high metal low acid copper baths, they have not solved problems inherent in electroplating of parts from high acid/low metal copper baths, U.S. Pat. No. 4,374,709 to Combs is a process for plating of copper on substantially non-conductive substrates utilizing high acid/low metal copper baths. While this process has been a great advance in the art of plating of non-conductive substrates, there remains a need for improved and simplified plating of metallic and non-conductive substrates and also in troublesome plating functions such as: plating of intricate parts with low current density areas; circuit board plating and other plating of substrates with surface imperfections; and in barrel plating applications.
For instance, barrel plating has been fraught with problems with regard to copper plating of parts. Typically, barrel plating operations have suffered from lack of proper adhesion between the built up layers of copper plate on the parts. Thus, barrel plating of parts has not been suitable from a production or sales standpoint. Copper plating applied on intricately shaped parts has been fraught with adhesion problems during thermal expansion cycles; thickness deficiencies in low current density areas; and suffer because of the low ductility of the deposit produced. Additionally, with respect to non-conductive plating of perforated circuit board material, or other substrates with substantial surface imperfections, the leveling properties of past plating methods have not been sufficient to overcome such surface imperfections in these substrates.
Thus, it has been a goal in the art to produce an electroplating bath and process which provides improved ductility copper deposits; has superior leveling and adhesion characteristics; and which has improved throwing power, beneficial in areas of low current density.